JPH0558933B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a center differential lock device for a four-wheel drive vehicle.

(Technical Background of the Invention and Prior Art) In a four-wheel drive vehicle, a front differential is provided between the left and right wheels on the front side to allow differential movement between the wheels, and a front differential is provided between the left and right wheels on the rear side. In addition to a rear differential that is provided to allow differential movement between the wheels, a propeller shaft that connects the front differential and the rear differential is provided with a propeller shaft that connects the front left and right wheels. It is equipped with a center differential that distributes the differential between the left and right rear wheels and allows differential movement between the front and rear wheels.

Furthermore, this center differential has
A center differential lock device is provided to regulate the differential rotation of the center differential as necessary, and when the vehicle is normally running, the center differential lock device is inactive and the differential rotation of the center differential is controlled. (i.e., the center differential is unlocked) to improve fuel efficiency and reduce running noise, but if the wheels slip (or if slip occurs), such as when driving on muddy ground or when accelerating. Or, when braking, if the force of the brakes differs between the front and rear wheels due to a load imbalance between the front and rear wheels, the center differential lock device is activated to adjust the center differential. Differential rotation is restricted (that is, center differential lock state), and safe driving is ensured by rotating the front wheels and rear wheels one-on-one.

However, in conventional center differential lock devices, the driver must manually switch between locking and unlocking, making it difficult to operate the center differential lock accurately depending on the vehicle's driving conditions. Therefore, in some cases, the safe driving of the vehicle may be hindered due to a driver's operational error.

Incidentally, there are conventionally known systems that determine which wheel is currently slipping by measuring and comparing the rotational speed of each wheel, and informing the driver of this (for example, Unexamined Japanese Patent Publication 1987-
(Refer to Publication No. 90217), this known example only detects the slip state of the wheels, and the subsequent operation of the center differential lock device is still performed by the driver himself, so it is said to improve driving safety. There is room for improvement in this respect.

On the other hand, although it is not a center differential lock control for a center differential of a four-wheel drive vehicle, Japanese Patent Application Laid-open No. 11922/1983 describes the following as shown in Figure 4:
When performing differential lock control on the differential 52 provided between the drive wheels 51, 51, the rotation speeds of the two drive shafts 53, 54 to which power is distributed by the differential 52 are measured by wheel speed sensors 55, 56, respectively. A technology has been proposed that enables automatic control by detecting the slip state by detecting the difference in rotation and determining the slip state from the rotation difference, and performing defrock control based on the determination signal.

When such a control concept is applied to the center differential lock control of a four-wheel drive vehicle, for example, as shown in FIG. The rotation speeds of the shaft 75 and rear shaft 76 are detected by wheel speed sensors 77 and 78, respectively,
It is conceivable that the center differential 67 is locked when a rotational difference occurs between the shafts 75 and 76. In FIG. 5, numerals 61 and 62 are front wheels, 63 and 64 are rear wheels, 65 is a front differential, and 66 is a rear differential.

However, when such a configuration is adopted, there are problems particularly in terms of running performance on rough roads and maneuverability, as described below. That is, during normal driving,
As shown in FIG. 6, the front wheels 61, 62 and the rear wheels 63, 64 have the same rotational speed, and no difference in rotation occurs between the front shaft 75 and the rear shaft 76. From this state, as shown in FIGS. 7 and 8, when the front wheels 61 and 62 enter a split road where the road surfaces have different μ values, the front differential 65 changes the differential between the front wheels 61 and 62. Since the front wheels 61 and 62 are accommodated, a difference in rotation occurs between the front wheels 61 and 62.

In this case, as shown in Fig. 7, when the degree of road surface split is relatively small, even if there is a rotation difference between the front wheels, the value is relatively small, and the rotation difference between the front shaft 75 and rear shaft 76 of the propeller shaft is It does not reach the point where there is a difference. Therefore, the center differential 67 is maintained in an unlocked state that allows differential rotation.

On the other hand, as shown in FIG. 8, when the degree of road surface split further progresses and the rotational difference between the front wheels 61 and 62 further increases, a rotational difference occurs between the front axle 75 and the rear axle 76. For the first time, the center differential 67 is locked and the front shaft 75 and rear shaft 76 are coupled one-on-one.

That is, when the center differential 67 is subjected to differential lock control based on the rotational difference between the front shaft 75 and the rear shaft 76, the front wheels 6
Even if there is a differential between the front shaft 75 and the rear shaft 76, and a center differential lock should be executed, the center differential lock will not be executed until a rotation difference occurs between the front shaft 75 and the rear shaft 76. , the timing of the center differential lock is delayed.

If the timing of the center differential lock is delayed in this way, the wheels will completely slip and the vehicle will become stuck, resulting in a rotational difference between the front axle 75 and the rear axle 76, which will deteriorate the drivability on rough roads. At this point, the clutch is engaged and the center differential is locked, so there is a large energy loss when the clutch is engaged.During the driving period when the front wheels are differentially engaged, the steering characteristics fluctuate greatly, and the steering stability of the vehicle is affected accordingly. This may cause problems such as lowering the temperature.

(Object of the Invention) In view of the above-mentioned problems, the present invention provides a center differential lock control system for a four-wheel drive vehicle that can automatically perform center differential control of a center differential more quickly and precisely. This was done for the purpose of providing equipment.

(Structure of the Invention) As illustrated in FIG. 1, the center differential lock device for a four-wheel drive vehicle of the present invention transmits power transmitted from an engine 9 through a transmission 10 to front left and right wheels 1 and 1. In a four-wheel drive vehicle equipped with a center differential 8 that distributes between the left and right wheels 2, 2 on the rear side, the center differential 8 is provided between the left and right wheels 1, 1 on the front side and allows differential rotation between the wheels. the front differential 6, the rear left and right wheels 2,
a rear differential 7 provided between the two wheels to allow differential rotation between the wheels; and a rear differential 7 provided between the left and right wheels 1, 1 on the front side and the left and right wheels 2, 2 on the rear side, respectively. wheel speed detection means 11, 11, . . . such as a wheel speed sensor that detects the rotational speed of the wheels, and reference wheel speed calculation means 4 that calculates a reference wheel speed based on signals from the wheel speed detection means 11, 11, .
3, a wheel condition detecting means 41 for detecting the slip condition of each wheel according to the difference between the reference wheel speed and the wheel speed of each wheel; and upon receiving a slip signal from the wheel condition detecting means 41, the center The present invention is characterized in that it includes an actuator control means 42 that sends a differential signal for performing a center differential lock to a locking actuator 13 that regulates the differential rotation of the differential 8.

(Function) According to this configuration, the wheel speeds of all four wheels, ie, the front left and right wheels 1, 1 and the rear left and right wheels 2, 2, are detected by the wheel speed detection means 11, 11, . . . A reference wheel speed is calculated by the reference wheel speed calculation means 43 based on each detected wheel speed, and the difference between this reference wheel speed and the detected wheel speed of each wheel is constantly monitored by the wheel state detection means 41. When any of the four wheels is in a slip state or a braking state, the wheel state detection means 41 immediately detects this as a difference between the reference wheel speed and each detected wheel speed, A slip signal is output to the actuator control means 42 to cause the locking actuator 13 to perform center differential locking.

(Embodiment) Hereinafter, the center differential lock device for a four-wheel drive vehicle of the present invention will be explained based on FIGS. 2 and 3. FIG. 2 shows a center differential lock device according to an embodiment of the present invention. A system diagram of a drive system of a four-wheel drive vehicle is shown, and in the figure, reference numeral 1 indicates the front wheels of the vehicle, and reference numeral 2 indicates the rear wheels.

Of each front wheel 1, 1 and each rear wheel 2, 2, each front wheel 1, 1 is connected by a front wheel axle 3 with a front differential 6, and each rear wheel 2, 2 is connected by a rear differential 7. They are each connected by a rear wheel axle 4 provided therein. Further, the front differential 6 and the rear differential 7 are arranged so that the front shaft 5A located on the front differential 6 side and the rear shaft 5B located on the rear differential 7 side are connected to each other by the center differential 8. The center differential 8 is connected to the front differential 6 and the rear differential 7 by a propeller shaft 5 which is connected to the center differential 8. are distributed respectively.

In addition, center differential 8 and rear axle 5
A multi-disc clutch 12 is installed between the clutches B and 12. The multi-plate clutch 12 is appropriately controlled to engage and disengage by an actuator 13 that is operated in response to a signal from a controller 40, which will be described later. When the actuator 13 is turned on, the multi-plate clutch 12 is engaged and the differential rotation of the center differential 8 is restricted, and the front shaft 5A and rear shaft 5B are connected one-to-one.
On the other hand, when the actuator 13 is turned off,
The multi-disc clutch 12 is disengaged, differential rotation of the center differential 8 is permitted, and the front shaft 5A and rear shaft 5B are rotated at predetermined rotation ratios.

Further, each front wheel 1, 1 and each rear wheel 2, 2 are provided with wheel speed sensors 11, 11, . . . for detecting their rotational speeds.
(corresponds to the wheel speed detection means in the claims)
are installed respectively. Signals from the respective wheel speed sensors 11, 11, . . . are inputted to a controller 40, which will be described later, as a center differential lock operation signal.

As shown in FIG. 3, the controller 40 includes four waveform shapers 21, 21, . . . that receive signals from the respective wheel speed sensors 11, 11, . and four counters 22, 22, .
Four latch circuits 23, 23, . . . which latch the data output from 22, . an adder 27 that adds the wheel speed data of each wheel output from each of the latch circuits 23, 23, . a divider 28 (corresponding to reference wheel speed difference means in the claims) for calculating the current average wheel speed (corresponding to the reference wheel speed in the claims); and each of the latch circuits 23, Four subtractors 24, which subtract the current wheel speed of each wheel output from 23,... and the average wheel speed output from the divider 28, and output the difference in wheel speed (differential speed) for each wheel. 24, . . . and a wheel whose differential speed is larger than a preset value (differential speed width) (that is, in a slip state) or the setting If even one of the four wheels is smaller than this value (that is, in a braking state), it is determined that it is necessary to lock the center differential 8, and the actuator 1 is immediately activated via the amplifier 30.
3 and a determination circuit 29 (corresponding to wheel condition detection means and actuator control means in the claims) which outputs an operation signal (center differential lock signal). Note that this determination circuit 29 is
Manual lock switch 14 installed on the driver's seat side is turned on.
When operated, a center differential lock signal is output to the actuator 13 regardless of the wheel speed of each wheel.

In a four-wheel drive vehicle equipped with a center differential lock device configured as described above, for example, during normal driving with the center differential 8 set to the unlocked state, the rear wheels 2,
When one of the wheels 2 enters mud or the like, the front differential 6 allows differential movement between the rear wheels 2 and 2, causing slippage in the rear wheel 2 that entered the mud. Then, upon receiving a wheel speed signal from the wheel speed sensor 11 provided on the rear wheel 2, the determination circuit 29 of the controller 40 determines that the rear wheel 2 is in a slip state based on the difference between the average wheel speed and the detected wheel speed. is detected, and the determination circuit 2
Actuator 13 receives an activation signal from 9 and performs a center differential lock operation, and center differential 8 is locked. Therefore, even though the rear wheels 2 are in a slip state, the front wheels 1, 1 are rotated by receiving power from the engine 9.
This makes it easy to get the vehicle out of the mud.

Also, when the vehicle slips during acceleration, the existence of a slipping wheel is detected from the difference between the average wheel speed and each wheel speed, and the center is moved in response to this slip signal. By locking the differential 8, acceleration is performed safely and smoothly.

On the other hand, if a braking operation is performed while driving at high speed in an unlocked state, in principle, the same amount of braking force is applied to each wheel, so all wheels must stop at the same time. Since the load sharing is different between the front wheels 1, 1 and the rear wheels 2, 2, for example, in a front engine vehicle, the rear wheels 2, 2 with the smaller wheel weight are compared with the front wheels 1, 1 with the larger wheel weight. There is a risk that a so-called single-lock state in which the vehicle stops earlier than the vehicle speed will occur, impairing driving stability and deteriorating braking performance.

However, in this embodiment, when a single lock state occurs, the determination circuit 29 of the controller 40 detects the single lock state based on the difference between each wheel speed and the average wheel speed, and in response, the actuator is immediately activated. 13, the center differential 8 is locked, and the front wheels 1, 1 and rear wheels 2, 2 are locked.
and are simultaneously braked at the same deceleration rate. Therefore, no spin phenomenon occurs, and the running stability and braking performance of the vehicle are improved.

Further, in this embodiment, as described above, the center differential lock control of the center differential 8 is performed based on the difference between the wheel speed of each wheel 1, 1, 2, 2 and the average wheel speed. Therefore, the front shaft 5A and rear shaft 5B of the propeller shaft 5
Center differential lock control is executed more quickly in response to changes in wheel conditions before a rotation difference occurs between the two wheels. Therefore, when driving on a low-grade split road as shown in FIG. 7, for example, the front left and right wheels 1, 1 or the rear wheels are This is particularly effective when there is a time lag between the time when a differential occurs between the left and right wheels 2, 2 and the time when a differential occurs between the front shaft 5A and the rear shaft 5B of the propeller shaft 5. be.

(Effects of the Invention) As is clear from the above description, the center differential lock device for a four-wheel drive vehicle of the present invention detects the slip state of the wheels by calculation from the wheel speed of each wheel, and automatically locks the center differential. Since the system controls the locking and unlocking operations of the differential, the center differential locking and unlocking operations are controlled. The locking/unlocking operation of the allencial can be performed accurately according to the wheel condition, and the effect of improving driving safety is obtained.

Furthermore, the reference wheel speed is determined based on the wheel speed of each wheel, and the slip condition is determined from the difference between this reference wheel speed and each wheel speed mentioned above to perform center differential lock control. Since the center differential is locked at a stage before differential rotation occurs between the axle and the rear axle, that is, at a stage where slip etc. occur in one of the wheels, for example, the above-mentioned known example is applied. Compared to a case where the center differential lock is executed at the stage when a differential is generated in the propeller shaft, such as in a center differential lock device of a four-wheel drive vehicle, the center differential lock control can be performed more quickly and finely. In particular, it is possible to obtain the effects of improving speed and handling performance on rough roads.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram of a center differential lock device for a four-wheel drive vehicle according to the present invention, FIG. 2 is a system diagram of a center differential lock device for a four-wheel drive vehicle according to an embodiment of the present invention, and FIG. Fig. 2 is a block diagram of the controller, Fig. 4 is an explanatory diagram of a conventional general differential device, and Fig. 5 is an explanatory diagram of the case where the differential device shown in Fig. 4 is applied to a four-wheel drive vehicle. , and FIGS. 6 to 8 are explanatory views of the operation of the center differential lock device shown in FIG. 5. 1...Front wheel, 2...Rear wheel, 3...Front wheel axle, 4
... Rear wheel axle, 5 ... Propeller shaft, 6 ... Front differential, 7 ... Rear differential, 8 ... Center differential, 9 ... Engine, 10 ... Transmission, 11 ...
Wheel speed sensor (wheel speed detection means), 12... Multi-plate clutch, 13... Actuator, 14... Manual lock switch, 40... Controller, 41... Wheel condition detection means, 42... Actuator control means, 43 ...Reference wheel speed calculation means.

Claims (1)

[Scope of Claims] 1. A four-wheel drive vehicle equipped with a center differential that distributes power transmitted from an engine through a transmission to left and right wheels at the front and left and right wheels at the rear, comprising: a front differential provided between the left and right wheels to allow differential rotation between the wheels; a rear differential provided between the left and right wheels on the rear side to allow differential rotation between the wheels; wheel speed detection means provided on each of the left and right wheels on the front side and the left and right wheels on the rear side to detect the rotational speed of each wheel; and a reference wheel speed based on the signals from each of the wheel speed detection means. a reference wheel speed calculation means for calculating, a wheel condition detection means for detecting the slip condition of each wheel according to the difference between the reference wheel speed and the wheel speed of each wheel, and a slip signal received from the wheel condition detection means. a center differential lock device for a four-wheel drive vehicle, characterized in that the center differential lock device for a four-wheel drive vehicle is equipped with actuator control means for sending an activation signal for performing center differential locking to a locking actuator that regulates differential rotation of the center differential. .